This invention relates to adjustable support columns for seats, and more particularly to the mounting of seats on gas or pneumatic springs in such manner that the undesirable effects of side or non-axial loading are minimized.
Adjustable length support columns for mounting seats or stools on bases have become prevalent in institutional and commercial office furniture. Such support columns utilize gas or pneumatic springs which include essentially a pair of cylindrical telescoping members, one of which is connected to the underside of the seat and the other of which is connected to the base. The telescoping members are coupled by a gas or pneumatic spring. Developments in such coupling devices have thus far not effectively dealt with the objectionable effects of side or non-axial loads on the gas or pneumatic spring in such a manner as to ensure continued smooth operation of the device. Such side or non-axial loads occur when a person does not sit directly above the central longitudinal axis of the spring or support column. At such times, objectionable stress is placed upon the gas spring and more particularly, upon the point where the piston of the gas spring is attached to the base. These stresses frequently cause early failures in the gas or pneumatic springs, which result from either the binding between the piston rod and associated bearing surfaces, and/or the deformation of seals which result in the leakage of pressurized fluids and lubricants.
Two attempts to solving this problem are set forth in U.S. Pat. No. 3,711,054 to Bauer, and No. 4,485,996 to Beukema et al. The Bauer patent is illustrative of an attempt to minimize the stress problem by laterally displacing the gas spring piston rod with relation to the bottom of the support structure to which the free end of the piston rod is mounted. The results of this approach are only marginally effective in minimizing the stress problem since the longitudinal axis of the piston rod is no longer parallel to the axis of the support structure. Therefore the piston rod is not perpendicular to the lower swivel assembly and the action of the device is no longer smooth since the bottom shoulder of the piston rod does not properly contact or engage the swivel assembly bearing race. Further, the constant tipping of the piston rod with respect to the bearing race tends to cause deterioration of the bearing race and resulting improper operation of the swivel structure.
The Beukema et al patent illustrates another attempt to solve the side loading problem by providing an articulated joint between the upper portion of the pneumatic spring cartridge and the depending support post from the seat. This arrangement also fails to provide a satisfactory solution to the side loading problem because the operation is not smooth and binding frequently occurs.
The present invention, then, is directed to a coupling technique for mounting a seat on a base in such a manner that it is vertically adjustable and rotatable thereon and not subject to the objectionable effects of side loading as is the case in prior art devices. In general, in order to overcome the side loading problem the upper end of the tubular casing which depends from the seat platform rests upon the upper end of the gas spring cartridge in such a manner as to be radially movable or tiltable and rotatable with respect thereto. The support cylinder includes an annular bushing which normally holds the casing in vertical alignment; however, a slight tilt or radial shift thereof is possible responsive to side loading on the seat thereabove. Of primary importance in the present invention, the gas spring including the cartridge and piston, however, are maintained vertically erect and perpendicular to the lower mounting bearing at all times.
The lower end of the casing includes a retainer therein having an opening therethrough greater in diameter than the diameter of the gas spring piston rod and smaller than the diameter of the cartridge. Such construction prevents removal of the casing from the cartridge, yet allows for tilting of the casing relative to the cartridge and piston rod. The casing is supported on the upper end of the cartridge by means of swivel bearings so that the casing is rotatable thereon, and the piston rod is attached to the base of the support cylinder by means of a second bearing assembly which makes the gas spring rotatable with respect to the support cylinder. The upper end of the tubular member forming the gas cartridge leaves the cartridge pin exposed through an opening therein. The activating pin extends downwardly within the casing and engages the cartridge pin for activation thereof.
It should be noted here that the present invention is directed to a technique for coupling any type of gas cartridge between a seat and a base in such a manner as to negate the objectionable effects of side loading. The details of the gas spring are not critical to the invention; however, one type of gas spring which is known to be particularly adapted for use in conjunction with the present invention is that shown in applicant's co-pending application Ser. No. 671,292 filed Mar. 13, 1984 and entitled "Hydropneumatic Spring Cylinder," which application has now been issued as U.S. Pat. No. 4,616,812 issued Oct. 14, 1986.
It is therefore an object of the present invention to provide an improved coupling apparatus for joining the seat of a chair, such as an office chair, to a base in such a manner that it may be rotated and vertically adjusted.
It is another object of the present invention to provide an improved apparatus of the type described which negates the objectionable affects of side loading in such types of furniture.
Another object of the present invention is to provide an apparatus of the type described in which the seat and a tubular casing depending therefrom are, upon side loading, caused or permitted to tilt relative to the vertical axis of the gas spring and piston rod thereof.